In skeletal muscle, the dystrophin-glycoprotein complex is located at the sarcolemma and is composed of peripheral and integral membrane proteins. As a whole, this complex links the extracellular matrix to the intracellular actin cytoskeleton and provides structural stability to the sarcolemma during muscle contraction. Duchenne muscular dystrophy, the most common form of dystrophy, is caused by mutations in the dystrophin gene that result in loss of dystrophin protein and the entire dystrophin-glycoprotein complex. My research group has pioneered several key discoveries related to the function of sarcospan, an integral component of the dystrophin-glycoprotein complex. We have shown that sarcospan plays an important role in mediating protein interactions within this complex. Sarcospan affects communication between the dystrophin-glycoprotein complex and the extracellular matrix. Importantly, we demonstrate that mild sarcospan over-expression in mdx mice, which possess a mutation in the murine dystrophin gene, rescues muscular dystrophy by stabilizing expression of a complex of proteins that is functionally analogous to the dystrophin-glycoprotein complex. We propose to investigate the molecular mechanism(s) of SSPN-mediated amelioration of mdx phenotype and reveal the compensatory mechanisms that may mask a potentially interesting and enlightening phenotype in the SSPN-null mice. We will also complete our characterization of SSPN's `rescue effect'by examining muscle mechanics. Our hypothesis provides a mechanism for cross-talk between transmembrane/cytoskeletal complexes (i.e. integrins and DGC) that may illuminate how compensatory mechanisms are regulated. Results from each of the Aims will provide new information on the role of sarcospan as an important structural element within the dystrophin-glycoprotein complex and uncover new information on sarcospan's function in signaling and disease. PUBLIC HEALTH RELEVANCE Our proposal addresses questions related to how disruption of the dystrophin-glycoprotein complex causes Duchenne muscular dystrophy. During our previous funding period, we discovered that sarcospan, an integral component of the dystrophin-glycoprotein complex, is able to ameliorate dystrophin-deficient muscular dystrophy in mice. We plan to test the physiological properties of these mice and investigate the mechanisms of sarcospan amelioration.